Intentionally grown interfacial layer (IL) is used in order to arrange a good interface between the channel region and the gate insulator, especially with high-k dielectrics (e.g. HfO2, HfSiO4, ZrO2, ZrSiO4, etc.), and to suppress the mobility degradation of the channel carrier of metal-oxide-semiconductor field-effect transistors (MOSFETs).
However, when the channel region contains silicon germanium, the formation of IL very often results in dangling bond on the surface of IL. The dangling bond decreases electron mobility at the channel region. One way to remove the dangling bond is to epitaxially grow a cap layer on the channel region. An addition of the cap layer increases the thickness of the channel region, and device dimension has to compromise.